Zinc base alloy



Patented Apr. 19, 1949 OFFICE",

ZINC BASE ALLOY Hyman Bierman, Chicago, Ill., assignor of twenty-five per cent to Maurice Perlin No Drawing. Application September 9, 1947, Serial No. 773,080

Claims.

r This invention relates to a zinc base alloy and more particularly to a novel zinc base die-casting alloy having improved properties.

- Zinc base die-casting alloys as presently used for commercial die-casting purposes are composed of zinc and small amounts of aluminum, copper and magnesium. Minor amounts of impurities such as iron, lead, cadmium and tin may be tolerated in such alloys. In general, the permissible maximum content of iron which may be tolerated is 0.10%, of lead 0.007%, of cadmium, 0.005% and of tin 0.005%. The zinc used in these alloys is a relatively pure zinc preferably containing at least about 99.94% of zinc.

In general, the zinc base alloys presently being used commercially consist of from about 2.0- 10.0% aluminum, from about 0.033.50% copper, from about 0.01-0.30% magnesium, and the balance a high grade zinc metal usually containing at least about 99.94% zinc. The best of these commercially used alloys contain no more than about 2.0% copper, no more than about 4.50% of aluminum and no more than about 0.10% of magnesium.

The die-castings made from these prior art zinc base die-casting alloys suffer from the fact that they deteriorate markedly in the presence of moisture and because they undergo an intercrystalline corrosion due, apparently, to the presence of occluded oxygen and the phase changes which normally take place in such alloys. Due to the marked tendency of these prior art zinc base alloys to occlude oxygen, the die-castings made from these alloys do not have a desirably smooth surface sheen nor a sufliciently thick surface skin or case depth.

I have found that by incorporating in the prior art zinc base die-casting alloys described above minute critical amounts of beryllium that an alloy of improved fluidity results and that diecastings made from this new alloy have greater stability against deterioration, greater case depth, better surface sheen and otherwise improved properties than die-castings made from any of the prior art commercially used zinc base diecasting alloys.

The novel zinc base die-casting alloys of the present invention contain from approximately 0.00001% to 0.0001% of beryllium, the balance being high grade zinc, aluminum, copper and magnesium, as described above, preferably, of course, free from iron, lead, cadmium, tin and other impurities. A preferred amount of beryllium is approximately 0.000027% and a preferred range is from approximately 0.000020% to '2 0.000075%. Amounts of beryllium very slightly below approximately 0.00001% may be used since such amounts result in an improved zinc base alloy. Amounts of beryllium slightly above 0.0001% may be used with consequent improve,

' ment in the properties of the, zinc base alloys, but

amounts of beryllium substantially above 0.'0001% are objectionable because the resulting alloy is more diificult to cast and the casting made there from becomes unduly hardened and brittle.

The beryllium can be incorporated into my novel alloy in the form of the metal, but I prefer to incorporate it in the form of the commercially available beryllium-copper alloy consisting of 2.0% of beryllium and 98.0% of copper (2.0% Be-Cu).

In preparing the alloys of the present invention the zinc is melted in a steel or ironkettle and the desired amounts of aluminum, copper and magnisium are added to the molten zinc. The beryllium is then added to the molten mass. If the beryllium is added in the form of the 2.0% Be-Cu alloy, the amount of copper previously added to the molten zincmay, if desired, be less than the desired amount so that it and the copper later added in the form of the alloy should equal the desired amount. The berylliumjor 2.10% Be-Cu alloy may be preliminarily melted together with the aluminum and this molten mixture may be added to the molten zinc. Other methods of incorporating the beryllium in my alloys will suggest themselves to skilled workers in the art. It is to be understood that the method of incorporating the beryllium in the alloy forms no part of the present invention.

A preferred alloy in accordance with the present invention consists of 4.0% aluminum, 0.08% copper, 0.05% magnesium, 0.000027% beryllium, and the balance a high grade zinc metal containing 99.99% zinc.

Die-castings were made from the preferred alloy of the present invention and from a control alloy consisting of 4.0% aluminum, 0.08% copper, 0.05% magnesium, and the balance a high grade zinc metal containing 99.99% zinc. In test runs at room temperature the castings made from the alloy of the present invention showed approximately 3.70% higher yield strength and 11.60% higher tensile strength than the castings made from the control alloy. The impact strengths for both alloys Were high.

After the conventional steam test for a ten-day period the castings made from the alloy of the present inivention showed 8.40% loss in yield strength, 12.30% loss in tensile strength and 3 36.50% loss in elongation. The impact strength of the castings was still high. On the other hand, the castings made from the control alloy showed 10.50% loss in yield strength, 15.60% in tensile strength and 32.60% loss in elongation. The impact values of these castings were also still high.

"Plated parts made from the castingsmade from the alloy of the present invention and fromithe control alloy were tested in accordance with the standard procedures in the conventional salt spray cabinet. The results of this test showed that the plated parts made from the castings .embodying the alloy of the present invention .stood up 10% better than the plated parts made from castings'embodying the control alloy.

The casting made from thealloyof the present invention had a lighter surface and a smoother sheen than the casting made from the control alloy. Microscopic examination of the castings revealed that the case depth of the casting made from the alloy of the present invention was almost two times that of the casting made from the control alloy. The casting made from the alloy of the present invention was tougher and had a greater elongation than the casting made from the control alloy.

The casting made from the alloy of the present invention had an elongation in two inches of from 9:0 to 13.0%. This is to be contrasted with the A. S. T. M. requirement for the same allow minus the beryllium. of 4.70% in two inches.

,A comparison of the fluidity of the alloys subjected Lto'test showed that the alloy of the present invention had a greater fluidity than the control alloy. The castings made from the alloy of the I.

present invention were more nearly perfect and had a'better sheen than the control castings. As a result of the improved fluidity of the alloys of the present invention, the castings made therefrom shrink more uniformly and have less cold shot effects than have castings made from the prior. art zinc oase die-casting alloys.

- 1 am not prepared to state the exact reason for the unusually efficacious results obtained by utilizing beryllium in a zinc base alloy in the critically smallamounts specified above. However, it appears that the beryllium reduces and in .some

instances even eliminates the oxygen which is occluded in die-casting with the zinc base diecasting alloys of the prior art.

The essential constituents of the zinc base diecasting alloy of the present invention are zinc, aluminum, copper, magnesium and beryllium. In the claims the expression consisting of is intended to restrict the invention to an alloy composed cf the aforenamed metals; however, it is not to be construed as to exclude from the scope of the invention alloys which contain not onlythe named metals but tin, cadmium, lead and iron in maximum amounts, respectively, of 0.005%, 0.005%, 0.007% and 0.10 as impurities.

I claim:

1. A zinc base alloy consisting of 2.0 to 10.0% of aluminum, 0.03 to 3.50% of copper, 0.01 to 0.30% magnesium, approximately 0.00001% to 0.0001% of beryllium, and the balance zinc.

2. A zinc base alloy consisting of 2.0 to 4.50% of aluminum, 0.03 to 2% of copper, 0.01 to 0.10% magnesium, approximately 0.00001% to0.-0001 of beryllium, and the balance zinc.

3. A zinc base alloy consisting of 2.0 to 10.0% of aluminum, 0.03 to 3.50% of copper, 0.01 to 0.30% magnesium, approximately 0.000020% to 0.000075% of beryllium, and the balance zinc.

4. A zinc base alloy consisting of 2.0 to 4.50% or aluminum, 0.03 to 2% of copper, 0.01 to 0.10% magnesium, approximately 0.000020% to 0.000075% 01" beryllium, and the balance zinc.

5. A zinc base alloy consisting of 4.0% aluminum, 0.08% copper, 0.05% magnesium, approximately 0.000027% beryllium, and the balance zinc.

HYMAN BIERMAN.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 375,244 Germany May 8, 1923 663,274 Germany Aug. 2, 1938 698,617 Germany Nov. 14, 1940 840,188 France Jan. 11, 1939 

